The invention relates to a pneumatic control apparatus for an exhaust emission cleaning system of an internal combustion engine, wherein a controlled negative pressure is applied to a differential pressure responsive device, such as a diaphragm or a piston.
Modern internal combustion engines include various ones of an exhaust gas recirculation system, an ignition distributor timing delay system, a secondary air supply system, or a dashpot control system for reducing the generation of harmful exhaust gases such as hydrocarbons (HC), carbon monoxide (CO), and nitrous oxide (NOX).
It is generally desirable that the operation of the exhaust gas recirculating system, the ignition timing delay system, and/or the secondary air supply system be stopped or restricted during continuous high speed, high load, and idling conditions and during the initial engine warmup period, but be fully operable during frequently encountered low speed, low load and acceleration conditions during which large quantities of harmful gases are produced, and that the dashpot control system be operable during high speed conditions and stopped during low speed conditions.
The reason for this is as follows: The operation of the exhaust gas recirculation system or the distributor timing delay system during continuous high speed or high load conditions causes engine output power reduction, fuel consumption increase, and exhaust system overheating, and the operation thereof during continuous idling conditions causes idle stability deterioration, increased fuel consumption, and heat damage due to insufficient engine cooling air. The operation of these systems during engine warmup causes start performance deterioration, increased vibration, and engine instability. On the other hand, the operation of the secondary air supply system during continuous high speed of high load conditions causes overheating which reduces the durability of the various cleaning systems. The operation of the dashpot control system during low speed conditions causes poor engine braking.
To overcome such problems a number of apparatuses for controlling exhaust gas cleaning systems have been proposed, such as an apparatus for controlling the systems with electrical signals increasing the rpms, load, temperature, etc. of the engine which are electrically detected, and another apparatus for pneumatically controlling the systems according to changes in the engine rpms, load, temperature, etc. on the basis of the negative pressure appearing in the intake passage of the engine.
Such apparatuses require complex electrical control circuits which are expensive and unreliable; however, or complicated negative pressure control circuits and an increased number of costly thermosensers, timers, and the like.